New members of the polynuclear manganese family: MnMn single-molecule magnets and MnMn antiferromagnetic complexes. Synthesis and magnetostructural correlations

The synthesis, crystal structures and magnetic properties are reported for three novel mixed-valence tetranuclear [MnII2MnIII2(HBuDea)2(BuDea)2(EBA)4] (1), [MnII2MnIII2(HBuDea)2(BuDea)2(DMBA)4] (2) and undecanuclear [MnII3MnIII8O4(OH)2(BuDea)6(DMBA)8] (3) clusters, where H2BuDea is N-butyldiethanolamine, HEBA is 2-ethylbutyric acid and HDMBA is 2,2-dimethylbutyric acid. The compounds have been prepared through self-assembly reactions of manganese(ii) chloride with H2BuDea and respective carboxylic acid in methanol solution in air, affording 1 with HEBA, and 2 or 3 with HDMBA, depending on the experimental conditions. The single crystal X-ray analysis reveals that 1 and 2 have similar centrosymmetric structures based on the {M4(μ3-O)2(μ-O)4} core, while 3 discloses the unprecedented {M11(μ-O)4(μ3-O)12} one. The Mn4 complexes display single-molecule magnet (SMM) behavior with a S = 9 spin ground state and a high energy barrier Ueff/kB of up to 51 K. The magnetic properties of 2 are successfully modeled with JMnIII-MnIII/hc = 25.7 cm-1 and two JMnIII-MnII/hc constants of 3.1 and -0.93 cm-1 (data correspond to the Ĥ = -Jŝ1·ŝ2 formalism). The Mn11 cluster exhibits a paramagnetic behavior with dominant antiferromagnetic coupling. A possible influence of intermolecular effects and of different peripheries of the magnetic cores designed by using 2-ethylbutyrate (in 1) or 2,2-dimethylbutyrate (in 2) on the magnetic properties of 1 and 2 is discussed. The experimental magnetostructural correlations for the {MnII2MnIII2(μ3-O)2(μ-O)4} cores, supported by broken symmetry DFT calculations, disclose the X-MnIIIMnIII angle and MnIII-O distance (where MnIII-X and MnIII-O are axial Jahn-Teller bonds) as the structural factors having the strongest influence on JMnIII-MnIII exchange coupling. It is shown that two JMnIII-MnII constants are necessary for the correct description of magnetic exchange couplings in the {MnII2MnIII2(μ3-O)2(μ-O)4} tetranuclear unit.

Reis Conceição N. , Nesterova O.V.1 , Rajnák C.2 , Boča R.2 , Pombeiro A.J.L. 1 , Guedes Da Silva M.F.C. , Nesterov D.S. 3
NLM (Medline)
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  • 1 Centro de Química Estrutural, Instituto Superior Técnico, Universidade de Lisboa, Av. Rovisco Pais, Portugal
  • 2 Department of Chemistry, Faculty of Natural Sciences, University of SS Cyril and Methodius, Trnava, 917 01, Slovakia
  • 3 Centro de Química Estrutural, Instituto Superior Técnico, Universidade de Lisboa, Portugal. and Peoples' Friendship University of Russia (RUDN University), Av. Rovisco Pais6 Miklukho-Maklaya st.Moscow 117198, Russian Federation
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